LargeSpider

The Archons would be used as a "Shock and Awe" kinda unit, utilizing the freakish health and speed for cutting the enemies down while taking minimal damage but as well providing buffs for it's allies such as small aim or will buffs and at higher levels, inspiring troops to dodge. It could also gain a buff from how well the squad performs such as extra movement or increased critical chance if no-one in the squad misses for a turn. I would think that they would take longer to heal due to their bio-mechanical bodies. You should also do multiple pathways for how the archon can turn out in a similar way to the sharpshooter's gunslinger or sniper pathways, like a support leader or a predator skill trees where the predator would be a throwback to the old floaters.

I'm having trouble seeing how the faceless would be used, their shape shifters so id imagine you could disguise them as aliens/advent without suffering from the concealment line-of-sight from the enemies them selves but the mechanical enemies and the scanning towers would still have their line-of-sight. So would they be used for more stealth purposes? I mean their claws would essentially be useless end game so some sort of progression needs to be put there for balancing.

Maybe if you add some specialized weapons for the the viper such as a poison dart gun or a limited-use poison cloud spewer, the class would be more compelling to use, specializing the viper in slowly wearing down the enemies for the rest of the squad to finish off

Good, id imagine your planning something along the lines of the particle canon from EW since it does provide the correct animations

*Copy*

I want to also suggest treating the Mutons like shock troopers since they have a lot of health and start off with armor. Maybe bring back that good ol' blood call the support other Mutons in your pack as an innate ability as well as abilities which regenerate health, all Mutons have s*** aim maybe this can act as a balance for them. Mutons seem to be the units that would be a high priority threat and at higher levels become a bullet sponge that deals out a decent amount of damage but are highly susceptible to enemy support roles such as the shield bearers (Culling the damage from the Mutons) , vipers and even possibly sectoids due to the Muton's low will (should also make them resilient to morale shocks such as casualties and reinforcements but weaker to psi attacks) You could also make a variation of the old beserker's "move when hit ability" which can either work in your favor or lead your Muton into an ambush. A variation of the new bersker's enrage ability could be made but do more damage against the enemy that shot at you which could eventually turn into blind rage if that enemy manages to hit the Muton again or deal a large amount of damage.

I have an idea for the chryssalid, since they are essentially wild animals they would have trouble learning basic abilities such as conceal. This is where i suggest having some sort of implants, gene modifications or augmentations to allow them to do these abilities naturally such as glands that produce acid instead of poison or an ability similar to the camouflage from enemy within (enhanced conceal)